Calcutta, July 4: The Trinamul Congress today demanded the removal of Keshari Nath Tripathi as Bengal governor and accused him of transforming the Raj Bhavan into an "RSS shakha".

The Trinamul demand was made a few hours after Mamata Banerjee alleged a "threat" call from the governor.

The party pointed out that the Constitution -- Article 156 (1) states "the Governor shall hold office during the pleasure of the President" -- empowers Rashtrapati Bhavan to remove a governor.

"The governor used unacceptable language in his call to the chief minister. This is not the first time such a thing has happened in the past two years but today he crossed the Lakshmanrekha. There needs to be action and it needs to take place now," Derek O'Brien, Trinamul's leader in the Rajya Sabha, said this evening. He declined to disclose what transpired during the call.

Trinamul accused Tripathi of having flouted "constitutional propriety" and alleged misuse of his post for furthering the cause of the RSS-BJP parivar. "Under him, the sacred Raj Bhavan has become an RSS shakha and he has been acting like a shakha pramukh," said O'Brien. "It is time for him to go. The President needs to seriously consider this," he added.

Sources said a letter from the party's secretary-general Partha Chatterjee would be sent to the Centre, formalising the demand, by tomorrow. They said the party was not going to back down on the issue and was gearing up to take the matter to Delhi.

Senior Trinamul leader and cabinet minister Subrata Mukherjee said the language used was "highly inappropriate". "I take full responsibility in saying that the language he used was full of hatred and aimed at humiliating the honourable chief minister," said Mukherjee.

A former Speaker of the Uttar Pradesh Assembly, the 82-year-old Tripathi took charge as governor of Bengal in July 2014. According to Trinamul sources, over the past couple of years, the former Uttar Pradesh president of the BJP has repeatedly tried to embarrass the Bengal government over of law and order.

A senior member of the Bengal cabinet said that since Tripathi took charge, the state unit of the BJP had been treating the Raj Bhavan like a "club" where its leaders rush to lodge complaints at the drop of a hat.

He alleged that Tripathi would, based on such complaints and "biased inputs" from the saffron camp, often sought reports and demanded answers from Nabanna. He said such incidents have been steadily souring the ties between Mamata and Tripathi.

A Trinamul MP alleged that some of the things Tripathi said in the phone call made Mamata "livid" and she seriously mulled resignation over the incident.

"We have not seen her this livid in many, many years.... It was appalling, the things he said. Governors have to be reasonable and follow the middle path, shedding bias, like commentators in cricket," he said.

"She was actually considering quitting her post over this. But she is not the one who should have to. She was elected for a second term with a thumping majority by the 10 crore people of Bengal. She was not a nominated appointee by the favour of a political party. The people put her there."